An ignition device for an internal combustion engine is shown in German Patent No. 28 25 830. The ignition device uses a pnp-transistor in its output stage. The primary winding of an ignition transformer is coupled to the collector terminal of the transistor. The emitter terminal of the transistor is coupled to ground by a current measuring resistor. During the operation of the ignition device, there are high power losses at the output stage, which are removed from the collector terminal to a heat sink. However, the collector terminal must also be electrically insulated from the heat sink when a square-shaped voltage appears during the shut-down process. These opposing requirements have been fulfilled by using an electrically-insulating ceramic layer having good thermal conductivity located between the collector terminal and the heat sink. One problem with the ceramic layer, however, is that it makes the assembly of the ignition device considerably more expensive and often does not compensate for the alternating thermal stresses occurring particularly in high power ignition devices.
Ignition devices are also shown in French Patent Nos. 2,407,363 and 2,318,323, U.S. Pat. Nos. 3,945,362 and 4,106,462, and German Patent No. 3,231,125, wherein the emitter terminals of the transistors in the output stages are coupled to ground connections.